In BiCMOS technology, bipolar transistors are integrated with CMOS transistors within a single integrated circuit (IC) device. In integrating these two different technologies, it is generally desirable to build a bipolar device that performs at fast speeds. An important figure of merit to determine whether the device performs fast enough is the ft frequency.
The ft frequency is the frequency at which transistor has a current gain equal to one. A faster transistor will have a high ft. In order to produce a faster transistor, the emitter resistance and the base resistance must also be lower.